WD3 Explain the principles of weather

Suggested time: 6-8 hours

• Energy from the Sun drives Earth's weather systems through the uneven heating of the Earth's surface. The uneven heating occurs due to a combination of the 23.5° tilt of the Earth's axis and differences in the heat capacity and albedo of regions of the Earth's surface.
  
• The water cycle is the principle mechanism that facilitates energy and water transfer throughout the hydrosphere, lithosphere, and atmosphere.
  
• The atmosphere releases stored heat energy through the formation of precipitation, and absorbs energy through vaporization and melting.
  

Learning Objectives

1. Identify weather-related questions that arise from practical problems and one's previous life experiences. (COM)
   
2. illustrate how science attempts to explain weather phenomena through observation and experimentation. (TL)
   
3. Explore cultural and historical views on the origins and interpretations of weather. (PSD)
   
4. Identify and describe the characteristics of the atmosphere, hydrosphere, and lithosphere.
   
5. Describe and explain heat transfer within the water cycle.
   
6. Describe and explain heat transfer in the hydrosphere and atmosphere, and its effects on air and water currents.
   
7. Describe how the hydrosphere and atmosphere act as heat sinks within the water cycle.
   
8. Conduct activities to investigate heat transfer in the hydrosphere and atmosphere, in particular the energy transfer involved in phase changes and the corresponding effect on the weather.
   
9. Identify how and where the major types of precipitation form.
   
10. Explain the effects of the Coriolis force on planetary air and water currents.
    
11. Reflect upon how knowledge is developed and changed in science (e.g., how scientists build scientific theories/models). (CCT)
    
12. Show understanding of ideas by providing alternate phrasing, drawings and diagrams, modeling, writing, etc. (COM)
    

Enrichment Learning Objectives

1. Solve problems related to specific heat capacity.
   
2. Solve problems related to relative humidity.
   

Key Questions

1. What are the three primary methods of energy transfer?
   
2. How is energy transferred through the atmosphere and hydrosphere?
   
3. What are the characteristics of the atmosphere, hydrosphere, and lithosphere?
   
4. What effects does the heating and cooling of the atmosphere/hydrosphere/lithosphere have on wind and water currents?
   
5. What are the general weather patterns in North America/Canada/Prairies?
   
6. How do the Coriolis force and the jet stream affect Earth's wind and water currents?
   
7. What is the role of precipitation in weather dynamics?
   

Key Concepts

• The lithosphere is the solid, inorganic outer shell of the Earth.
  
• The hydrosphere is the waters of the Earth.
  
• The atmosphere is the gaseous envelope that surrounds the Earth.
  
• The atmosphere consists of multiple layers: troposphere, tropopause, stratosphere, mesosphere, thermosphere, and exosphere.
  
• Conduction is the transfer of energy through a substance by the collision of particles.
  
• Convection is the transfer of energy by the movement of particles in a fluid (liquid or gas).
  
• Radiation is the transfer of energy through space by waves.
  
• Heat capacity is a measure of how much energy is required to raise the temperature of a substance.
  
• Specific heat capacity is the amount of energy required to raise the temperature of one gram of a substance one degree Celsius.
  
• Albedo is a measure of a surface's ability to reflect light.
  
• Precipitation is water that falls to the ground in liquid or solid form.
  
• Drizzle is falling water droplets that have a diameter between 40 µm and 0.5 mm.
  
• Rain is falling water droplets that have a diameter between 0.5 mm and 5 mm.
  
• Sleet is ice pellets (frozen raindrops) that bounce upon impact with the ground.
  
• Snow is frozen water crystals that form below 0°C.
  
• Fog is water droplets, ice crystals, or smoke particles that collect near the Earth's surface and that reduce visibility to less than 1 km.
  
• Hail is frozen water droplets that are created by cycling through highly active thunderclouds many times.
  
• Dew is water vapour that condenses on cool surfaces near the Earth's surface, typically in the morning.
  
• A cloud is a collection of small water or ice particles occurring above the Earth's surface. Clouds are classified according to their height of occurrence and shape.
  
• The water cycle or hydrologic cycle is a model that describes the storage and movement of water between the atmosphere, hydrosphere, and lithosphere.
  
• The Coriolis Effect is the apparent change in direction of a moving object in a rotating system. In weather systems, this refers to the curvature of the prevailing wind systems (westerlies and trade winds) due to the Earth's rotation.
  
• Models (physical, mathematical, or conceptual) are simplified representations of real phenomena that facilitate a better understanding of some scientific concepts or principles.
  
• Scientific knowledge is generated by asking questions concerning the natural world.
  
• Scientific knowledge is based on experimentation and observation.
  
• Scientific results are reproducible if all other conditions are identical.
  
• Theories in science consist of a set of connected and internally consistent group of statements, equations, or models or a combination of these which serve to explain a relatively large and diverse set of phenomena.
  

Pre-Instructional Questions

1. Do students understand the three methods of energy transfer - conduction, convection, and radiation?
   
2. Are students able to describe why seasons occur on Earth?
   
3. Are students able to describe the characteristics of the atmosphere, hydrosphere, and lithosphere?
   
4. Are students able to describe the role of energy transfer in the water cycle?
   
5. Are students aware of the general weather patterns in Canada and in their region?
   
6. Do students understand global wind patterns?
   
7. Do students understand how the Coriolis force influences global wind and water patterns?
   
8. What types of precipitation are students able to identify?
   

Suggested Teaching Strategies and Activities

1. Some of the suggested activities for supporting student achievement of this foundational objective include the building of models to represent weather-related phenomena. Teachers may choose to have small groups research and create different models and then present the models to the class at an appropriate time in the unit. The class could discuss the role of models in science as a means of understanding features of abstract concepts and the limitations inherent in all models (physical, conceptual, or mathematical).
   
   
2. Students could discuss or investigate weather-related questions that require an understanding of the scientific principles of weather to answer. For example:
   
   • Why can you see your breath in the winter?
   • Why are snowflakes sometimes small and sometimes large?
   • Why is fog sometimes thick and sometimes thin?
   • What are the differences between ice crystals and snow crystals?
   • Why does the temperature often rise on a cold day when it begins to snow?
   • Do air, soil, and water increase in temperature at the same rate when they are heated?
   • How do large bodies of water or land influence the weather?
   • How does the jet stream influence Canadian weather?
   • Can any two snowflakes be alike?
   • Can rainbows occur in the winter?
   • What is the difference between drizzle and rain?
   • Why do global wind and water currents tend to move in certain directions?
   
   
3. Students could examine weather folklore or sayings from a variety of cultures and identify similarities and differences in the sayings, expressions, rhymes, myths, or legends that relate to explanations of weather. Students should also look for similarities and differences in the ways that various cultures attribute control of the Sun, moon, winds, rain, snow, and other weather features to the actions of spirits and gods. Students should recognize the relationship between culture and lifestyle, exploring the influence culture can have on the views and opinions of people. (COM, PSD, CD 9.3)
   
   
4. Students could construct models that represent the composition and organization of the layers of the atmosphere (troposphere, stratosphere, mesosphere, thermosphere, and exosphere). Models should identify the temperature and density characteristics of each layer.
   
   
5. Students should conduct activities to demonstrate the three methods of energy transfer (conduction, convection, and radiation) in solids, liquids, and gases. These activities should model the similarities and the differences in rates and processes between heat transfer in air, water, and soil. Students should relate heat transfer in solids, liquids, and gases to temperature changes in the lithosphere, hydrosphere, and atmosphere. Students should be able to explain the different heating and cooling rates and processes that occur in each 'sphere'.
   
   
6. Students could conduct an activity to determine the relative specific heat capacities of various objects (i.e., 100 g of water, 100 g of steel, 100 g of dry soil, or 100 g of wood). The emphasis of this activity is that students understand some materials absorb and release different quantities of heat per unit mass than other materials. It is important for students to realize that water has a relatively high capacity compared to most common substances and to understand the effect this has on the weather, particularly as a moderator. It is not necessary that students develop or use the formula for specific heat capacity. (NUM)
   
   
7. Students could conduct experiments to determine which properties determine the amount of solar energy that materials absorb or reflect. Students might test properties such as color, shape, texture, density, or material and then relate the results to the physical features of the Earth in their community and throughout Canada .
   
   
8. Students could create a model of the Earth's energy budget to illustrate the distribution of incoming solar energy as it enters the Earth's atmosphere. The model should indicate the typical percentages of solar energy that are absorbed or reflected in each interaction. Students could use their models to demonstrate their understanding of objectives related to climate change or sustainability.
   
   
9. Students could construct a model of the water cycle (models may be physical or conceptual) and explain the salient features of the cycle. Given that students have likely already seen or constructed models of the water cycle in previous grades, students should extend their understanding by including the water budget (the percentage of water in each portion of the cycle) as part of the model. Students should also be able to explain the water cycle at global and regional levels, particularly the moderating effect of large bodies of water on local and regional weather.
   
   
10. Students could write the story of a water particle that travels through the water cycle in order to explain the salient features of the water cycle. Students should show that any given water particle will not likely travel through the entire cycle in one single pass but instead may travel through portions of the cycle multiple times before completing an entire journey. (COM)
    
    
11. Students could explain how clouds are an indicator of the type of weather that is occurring, or will likely occur. Explanations should differentiate between cloud types, their general altitudes, their characteristics, and the type of weather they indicate.
    
    
12. Students should describe the following types of precipitation and the conditions under which they occur: fog, frost, snow, rain, sleet, hail, dew, and drizzle. Student descriptions should relate the formation of each type of precipitation to energy transformations in the water cycle.
    
    
13. Students could conduct an activity to determine the relative humidity of the air in a variety of locations. Students should then be able to identify the factors that influence relative humidity.
    
    
14. Students could create a model to illustrate the different types of weather fronts (warm, cold, and occluded). The model should explain temperature and pressure differences and air movement within each type of front.
    
    
15. Saskatchewan students should have sufficient experience with winter to recognize that the temperature often rises noticeably when it begins to snow. This may appear to be paradoxical to students, who also recognize that temperatures need to be below the freezing point of water for snow to form. Students could investigate this discrepancy and explain how this phenomenon is related to latent heat in the atmosphere. (TL)
    
    
16. Students could create a model to illustrate global wind and water circulation patterns, and the role of the Coriolis force in causing these patterns. Such a model can help explain the occurrence of phenomena such as the jet stream, westerlies, doldrums, trade winds, Gulf Stream , and warm and cool ocean currents. (CCT)